# Mega-

Mega is a unit prefix in metric systems of units denoting a factor of one million (10$^6$ or 1000000). It has the unit symbol M. It was confirmed for use in the International System of Units (SI) in 1960. Mega comes from Ancient Greek: μέγας, romanized: mégas, lit. 'great'.

## Common examples of usage

* Megapixel: 1 million pixels in a digital camera
* One megatonne of TNT equivalent amounts to approx. 4 petajoules and is the approximate energy released on igniting one million tonnes of TNT. The unit is often used in measuring the explosive power of nuclear weapons.
* Megahertz: frequency of electromagnetic radiation for radio and television broadcasting, GSM, etc. 1 MHz = 1,000,000 Hz.
* Megabyte: unit of information equal to one million bytes (SI standard).
* Megawatt: equal to one million watts of power. It is commonly used to measure the output of power plants, as well as the power consumption of electric locomotives, data centers, and other entities that heavily consume electricity.
* Megadeath: (or megacorpse) is one million human deaths, usually used in reference to projected number of deaths from a nuclear explosion. The term was used by scientists and thinkers who strategized likely outcomes of all-out nuclear warfare.

## Exponentiation

When units occur in exponentiation, such as in square and cubic forms, any multiples-prefix is considered part of the unit, and thus included in the exponentiation.
* 1 Mm$^2$ means one square megametre or the size of a square of 1000000m by 1000000m or 10$^{12}$m$^2$, and not 1000000square metres (10$^6$ m$^2$).
* 1 Mm$^3$ means one cubic megametre or the size of a cube of 1000000m by 1000000m by 1000000m or 10$^{18}$ m$^3$, and not 1000000cubic metres (10$^6$ m$^3$)

## Computing

In some fields of computing, mega may sometimes denote 1048576 (2$^{20}$) information units, for example, a megabyte, a megaword, but denotes 1000000 (10$^6$) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s. In the case of 3½-inch floppy disks, sizes were given in megabytes of 1000KB or 1024000 bytes. The prefix mebi- has been suggested as a prefix for 2$^{20}$ to avoid ambiguity.
SI prefixesvte :
| Prefix | Prefix | Base 10 | Decimal | Adoption |
| Name | Symbol | Base 10 | Decimal | Adoption |
| quetta | Q | 10$^{30}$ | 1000000000000000000000000000000 | 2022 |
| ronna | R | 10$^{27}$ | 1000000000000000000000000000 | 2022 |
| yotta | Y | 10$^{24}$ | 1000000000000000000000000 | 1991 |
| zetta | Z | 10$^{21}$ | 1000000000000000000000 | 1991 |
| exa | E | 10$^{18}$ | 1000000000000000000 | 1975 |
| peta | P | 10$^{15}$ | 1000000000000000 | 1975 |
| tera | T | 10$^{12}$ | 1000000000000 | 1960 |
| giga | G | 10$^9$ | 1000000000 | 1960 |
| mega | M | 10$^6$ | 1000000 | 1873 |
| kilo | k | 10$^3$ | 1000 | 1795 |
| hecto | h | 10$^2$ | 100 | 1795 |
| deca | da | 10$^1$ | 10 | 1795 |
| — | — | 10$^0$ | 1 | — |
| deci | d | 10$^{−1}$ | 0.1 | 1795 |
| centi | c | 10$^{−2}$ | 0.01 | 1795 |
| milli | m | 10$^{−3}$ | 0.001 | 1795 |
| micro | μ | 10$^{−6}$ | 0.000001 | 1873 |
| nano | n | 10$^{−9}$ | 0.000000001 | 1960 |
| pico | p | 10$^{−12}$ | 0.000000000001 | 1960 |
| femto | f | 10$^{−15}$ | 0.000000000000001 | 1964 |
| atto | a | 10$^{−18}$ | 0.000000000000000001 | 1964 |
| zepto | z | 10$^{−21}$ | 0.000000000000000000001 | 1991 |
| yocto | y | 10$^{−24}$ | 0.000000000000000000000001 | 1991 |
| ronto | r | 10$^{−27}$ | 0.000000000000000000000000001 | 2022 |
| quecto | q | 10$^{−30}$ | 0.000000000000000000000000000001 | 2022 |
| Notes ↑ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873. |||||